A while ago, Francesca from Element 14 kindly contacted me to ask if I wanted to receive some products from their catalog for review. I said yes and since I already had a wishlist going on (as most electronics guys have) it was easy to pick up some products. I also considered current and future projects when picking the items and so I had 4 items:

I asked for the STM32VLDISCOVERY because I wanted to play with one of these ever since I discovered this STM32 book written by Geoffrey Brown. The book seems so nicely written and from a practical point of view seems like it will get me started and working on the STM32 in no time. I’m also working on a couple of projects right now for which the STM32 might seem like overkill but I might use it anyway just build some experience around this chip.

I asked for the ATXMEGAA3BU-XPLD because it is a nice platform all around. The MCU is the ATxmega256A3BU and you also get some analog sensors, an lcd display and lots of IO’s. Excellent for when you need to throw something together and test it on an Atmel ATXmega. The ATSAM4L-XPRO which I received in error, features Atmel’s ATSAM4LC4C Cortex-M4 MCU which is nonetheless interesting in the industry but isn’t of much use to me on it’s own without some expansion board.

The TPS54231EVM-372 and TPS5450EVM-254 from Texas Instruments were requested because I use both of these in two of my projects and I wanted to have a reference testing platform for comparison to my own implementation in layout and design. I use the TPS54231 in the new Audio Spectrum Analyzer to power the digital/LED section and I use the TPS5450 in my DIY digital power supply as the switching  pre-regulator before going into a linear reg.

More will follow on these as I am going to perform some measurements like output noise on the TPS54231EVM-372 and TPS5450EVM-254 using my entry level scope and compare the results with the ones from the datasheet.

Also if you would like to checkout more products from these manufacturers, see the Newark category pages:


Remember the Xprotolab XMEGA portable oscilloscope that I reviewed last year ? Well Gabriel Anzziani, the creator has put the project up on kickstarter:

The Xprotolab has been in development for several years, the hardware and firmware are stable. Now its time to put the device in an enclosure and add a rechargeable battery.

A case and a battery should complete the device and make it more attractive to carry in a toolbox. I know from experience, when I reviewed it. that I had to find a plastic enclosure to keep it in and powering it always required 2 extra wires from my circuit. So head-over to the kickstarter page to read more about the improvements.

July 22nd, 2012

USB A to micro USB bridge

USB to USB micro bridge

This is a little project I made recently, I call it USB A to micro USB bridge and it does what the name says: it’s just a bridge between the USB A female connector and the female micro USB. In the middle there is a DIL pin header that allows you to connect or disconnected individually the USB signals. I needed this because recently I started working on a USB project and I wanted to have an easy way to hook up a multimeter for measuring things like voltages or current passing through.

I have PCB’s from both Seeed and ITead for this little project because I wanted to compare their service and so I ordered from both of them. You can download Eagle sch and brd files in ZIP format from here.

USB-micro to USB-A bridge

As promised in my latest post I purchased the 5x5cm pcb prototype option from both Seeed and ITead in an attempt to compare the two services regarding PCB quality, e-test, shipping/processing times. As Ian from DP suggested in a comment the only difference I should expect to see is shipping/processing time. I’m more interested in finding scratch marks on the pads that would suggest they are using a flying probe machine for the e-test(this is related to my older post regarding ITead studio false 100% e-test).

I submitted both of my orders approximately at 12:00 AM June 13th 2012(GMT+1). The design I sent is the one pictured above and it is a USB micro to USB-A bridge. I plan to use it for measuring current draw from USB port. More specifically it will allow me to place a multimeter in series with VCC or GND.

The total from Seeed was $14 while the one from Itead was $13.90. The total from OSH Park $70 but it was for a totally different board(larger) so it’s not fit for comparing.

Starting from now it will probably take 4 weeks for the PCB’s to arrive. I’ll update this post when there is more info to share.

Update: Although its not fair to compare it to Seeed and ITead I also placed an order with OSH Park(also known as Laen, DorkbotPDX). Actually the order placed with OSH Park is not for the sake of comparison but more because it was related to another design for which I really needed a PCB to start developing with. So all 3 orders we’re placed same day, approximately around same hour also. Here are the results:


Seeed ITead OSH Park
Order placed June 13th 2012 June 13th 2012 June 13th 2012
Design sent to fab June 14th 2012 June 13th 2012 June 15th 2012
Order shipped June 20th 2012 June 19th 2012 July 2nd 2012
Order received July 9th 2012 June 28th 2012 July 10th 2012
Total 26 days 15 days 27 days



Seeed ITead Dorkbot
Ordering process 3 3 3
Duration 1 4 1
PCB quality 2 2 5
e-test probably probably probably

Ratings were given from 1 to 5, with 5 meaning excellent service.

Ordering process: I was planning on giving Dorkbot a 5 star rating for their ordering process. However that changed when I received the PCB’s from them with no silkscreen on them. They have a good idea but its not quite in its final form: you create an account on their website after which you can upload your gerber files and place an order. They do give a recommended naming convention for the gerber files and its entirely my fault for not following it which resulted in my silkscreen layers not being recognized by the service and thus they were not added to the panel. However I think the service should at least let the user know that it failed to recognize some of the files. I already talked about this with Laen(service admin) which explained that such a feature gives out plenty of errors for people who upload files generated from tools like Altium Designer which generate lots of other files except the standard ones. As a conclusion you should be careful to name your files using the recommended scheme. This way of ordering is fast but has to be intelligent enough to detect problems like mine, that’s why I’m only giving it a 3 star rating.

As for Seeed and Itead they both use the same method of ordering & paying an item from the online store after which you send an email with the order id containing your gerber files. This method is more time consuming.

Duration: I’m going to start commenting on ITead because this order went as smooth and as fast as possible, it left the others well behind in terms of speed. I think there is the possibility that they were watching the blog considering I posted about their pcb service in the past and that they made sure this order gets processed as soon as possible. I must say that previous orders from them took approximately 4 weeks to arrive same as with Seeed, nevertheless this time the PCB’s arrived in a record 15 days. Seed is second in this category with 26 days, followed by OSH Park with 27 days.

PCB quality: As it can be observed in the pictures bellow Seeed and ITead seem to be of identical quality and I’m giving them a 2 star rating. Truth be told you don’t need anything more for prototyping but if you plan on building something more serious and more if you plan on selling it I would recommend using something of better quality.  I also noticed the two had a slightly different shade of green for the soldermask but nothing to say about that as even different batches of PCB’s from the same fab can have different shades of silkscreen colour. A small difference was noticed in the silkscreen quality. As it can be observed in the following photo the PCB from seeed has a better quality silkscreen.

itead vs seeed silkscreen

One thing that I don’t like about Seeed and ITead is that they add text to your board. They do it so they can easily identify your pcb’s among others. Some people(me included) care about the looks of the PCB design and will be annoyed by this. As it can be observed in the following picture ITead adds the text in the silkscreen layer while Seeed adds it to the copper layer.

itead vs seeed order number


Comparing Seeed and ITead to OSH Park it’s not fair because OSH Park pcb’s have a more expensive ENIG finish (as well as overall more expensive service) which stand for Electroless nickel immersion gold. ENIG being a chemical process results in excellent surface planarity as opossed to HASL (hot air solder levelling) which leaves behind visible irregularities. However just as a review of the service and quality it can be seen in the pictures bellow that the quality of OSH Park pcb’s (purple soldermask) is top notch. The pads show a perfect finish and the soldermask apertures have excellent tolerance. In fact the text “beta” shown in the pictures bellow is placed in copper as well as in tStop layer. As it can be seen the soldermask aperture fits perfectly over the copper text. In conclusion OSH Park pcb’s can definitely be used for production so I give it a 5 star rating for quality.

E-test: This is a difficult subject. Seeed claims 50% e-test and 5 out of the 10 boards I received from them had been marked with some black stripes on the side. I’ve looked at all 10 under the microscope but I haven’t noticed anything different between them. If the e-test was indeed performed it must of been done before the HASL finish process.

ITead claim 100% e-test. In the envelope I found 11 pcb’s instead of the expected 10. I don’t know the exact reason, maybe they had extra space available and decided not to waste it. I’ve looked them all under the microscope and found them to be similar to the ones from Seeed. No easily visible scratch marks to indicate a post-production e-test. The following pictures shows the two under the microscope; some small marks can be observed on the connector pads, however I’m not sure they are really marks left by some kind of probe touching the PCB or if they are just small irregularities in the surface.

itead vs seeed possible test points

later update: In the video below we can see how the flying probe test is performed on Arduino pcb’s. Credits go to bunnie for recording the video. We can clearly see that the step is the final step in the PCB fabrication process so it would definitely leave scratch marks on the PCB.

As for OSH Park, I couldn’t find anything related to e-test on their website so not sure what to say.

later update: Laen who runs OSH Park explained that their fab doesn’t perform e-test. Instead, the fab uses AOI to QA every step of the process. In practice, this has resulted in a bad board rate of less than 1 in 10,000.

later update: Bradley Gawthrop who I follow on Twitter posted this picture of some boards he got recently. In the photo bellow we can clearly see the scratch marks left after the e-test has been performed. Only half of the pcb’s had the marks but this is as advertised by his manufacturer.

electrical test scratch marks

In conclusion both Seeed and ITead are great for prototypes. I think under normal conditions you will have your pcb’s in about 4 weeks since the day you ordered them. You can’t use them for any fine pitch stuff like BGA’s and don’t count on these being e-tested. For anything require fine pitch or higher overall quality you should go with OSH Park, you won’t be disappointed.

In the end here are some pictures of the PCB’s:

itead studio pcb

Today I got this email from Alex.Xie which is a Marketing Manager at Itead Studio:


Sorry to trouble you. We get some mails for asking about this blog http://www.youritronics.com/iteadstudio-false-electrical-test/ So , I thinks that I need to give out some reply about it.

First, sorry about the last mail, Sunny didn’t make it clear. Before, the factory just do the 50% e-test for 10 boards, and these 5 boards will be marked with stripe on the edage, we test the rest 50% without stripe ourselves. Now the factory will offer 100% e-test for all 10 boards, so there should be stripe on all boards.

Sunny just want to say that – e-tested or not, is nothing to do with the stripe on the edage. The stripe on edage is not a sign/mark of e-test. Sorry for our poor English and the wrong expression.

You can find more detailed about our e-test process here: http://dangerousprototypes.com/forum/viewtopic.php?f=2&t=3468&start=15.

While this clarifies the initial reply and explains what they meant it does not explain why we don’t see any tooling/scratch marks on the pads for PCB’s which are supposed to be e-tested. I think I will place one order with itead and one with seeedstudio, this will allow me to compare: quality,e-test,shipping time,order processing time.


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